No one knows or cares which side fired the first missiles, but once they were up, everyone else fired too. then, on October 23, 2077, the world ended in nuclear holocaust. Eventually, the two superpowers clashed over the Alaskan oil fields, hoping to secure just a little more of that black gold.
Unfortunately, the good times would not last: the world's inefficient technology depleted fossil fuels even faster than in the real world, causing massive resource wars to break out worldwide while China and the United States began hoarding their last fuel reserves. The shift towards nuclear energy gave way to technological wonders previously relegated to science fiction, from robot butlers to wrist-mounted computers. After World War II, the United States became an okay place to live.